Ultra Xfinity 600w 5vsb mod

[shovenose]

Re: Ultra Xfinity 600w 5vsb mod

Hmm... can't you just replace all the crap caps, then it wouldn't matter which one is the "killer" cap
Even thought you're going to have a killer time replacing all those little suckers

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

ok, i think i more or less have the circuit figured out:

• the transofromer goes to the large diode, which acts as a 1/4 bridge, creatign pused DC power
• from there, it goes to pin 1 of the optocoupler, the input of the coil, and the positive lead of the capacitor 1 (680uf 16v)
• the other side of the coil is connected to a load resitor (100 ohm), the positive lead of capacitor 2 (680uf 16v), and the 5vsb output
• the two capacitors and the load resistor connect to ground

from what i see, the two 680uf caps are the killer caps, especially capacitor 2. they also suppress ripple, depulsing the dc power coming from the diode and transformer.

therefore, the only idea i can think of is to change the load resistor (more watts at the least) and to find some high temp 'lytics' for the two capacitors. Right now I have my list set to nichicon HE, since other circuits use that value; however, I may look for soemhtign more temp resistant.

my analaysis correct?

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

well jeez, replacing all the little caps in this beast would take forever... it is full of tiny caps.

i thought he said secondary, my bad there.

noting on the primary side, connected to pin 1 of the optocoupler is the positive lead of the righthand 680uf 16v cap and the coil. on the other side of the coil is the positive lead of the other 680uf 16v cap. the negative leads of both caps are grounded.

the negative lead of the 10v 10uf cap is connected to the coil ^ via a diode.

the 100 ohm resistor in question is between the coil and ground, looks to be the loading resistor.

also worth noting is that pin 1 of the optocoupler is also connected to a bigass diode, which is connected to the 5vsb transformer.

it looks like I found the wrong cap... suggestions?

edit- the other side of the coil is also the 5vsb. that resistor is in fact the load resistor, and the 10uf 50v cap is likely out of circuit.

[momaka]

Re: Ultra Xfinity 600w 5vsb mod

it is... it is also near the 5vsb lead. also nearby are two 680uf 16V caps and a coil between them...

That's the secondary side, not the primary.

Killer cap is usually on the primary side, by the primary heatsink and 5vsb MOSFET as c_hegge mentioned. Not all 2-transistor 5vsb circuits have the killer cap, though. My Macron MPT-301 is an example of that.

Flip the PSU board and see where the traces for that 50v, 10uF cap are going to. If you see them going to the opto-coupler by the 5vsb transformer, then replace it. And if you don't, replace it anyways - Canicons aren't that great.

The two 16v, 680uF caps should also be replaced. 6.3v/10v @ 1000uF is usually more appropriate for that.
I'm also guessing R19 (100 Ohms, right by one of the 16v, 680uF caps) is the minimum load resistor for the 5vsb. If it's connected between 5vsb and ground, then that's what it is indeed. 100 Ohms is a good value, but if you have a 1W resistor or higher of that same value, then replace that as well. I believe the one in the current spot for R19 is 1/2 watt - probably gets pretty hot. Not good for the 16v 680uF 5vsb filtering cap near it. 1W should run a bit cooler.

[c_hegge]

Re: Ultra Xfinity 600w 5vsb mod

That's an interesting design. the killer cap is usually located somewhere in the red shaded area of the attached picture, but if there are no small caps there, my best guess would be the 10uf 50v in front of the two bigger ones (the one I think you've been referring to)

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

sure.



the components I spoke of are all in the foreground.

[c_hegge]

Re: Ultra Xfinity 600w 5vsb mod

Could we have a picture of the PCB from the back?

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

it is... it is also near the 5vsb lead. also nearby are two 680uf 16V caps and a coil between them... dang I wish I was better at psu modding...

[c_hegge]

Re: Ultra Xfinity 600w 5vsb mod

The killer 5vsb cap is usually near the primary heat sink toward the back of the PSU. If that's where it is on this power supply, then that could well be it.

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

and the 5vsb cap in question is likely the 50v 10uf one?

[c_hegge]

Re: Ultra Xfinity 600w 5vsb mod

I'm sure Nichicon HE would be fine. I use them all the time in power supplies, and they work every time.

EDIT: as for the 5vsb cap, I think 25v should be OK. some PSUs have 47uF@25v in that position. If in doubt you can check it with a DMM.

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

another question: for the other caps in the psu, is nichicon HE ok? I am having a hard time sourcing the two 6800 uf 16V caps in the unit; the only two brands with the size in a "low esr" format are Cornell Dubilier and lelon

[mockingbird]

Re: Ultra Xfinity 600w 5vsb mod

The only flaw with this idea I can think of is that I heard that polymer caps do not handle ripple well (But they do handle heat well - that's why PSUs with electrolytic caps fare better in ripple tests than polymer PSUs). But like you said, this cap is not there to suppress ripple, it's there to take an unreasonable amount of heat.

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

so have I ID'd the correct cap that needs fixed? the 50v 10uf? (highest voltage I can get is 25v, will that be high enough?)

[everell]

Re: Ultra Xfinity 600w 5vsb mod

I suggest that you try your idea, then report back to us on your results. Let us know if it stops the squealing.

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

perhaps, like this?

http://www.mouser.com/ProductDetail/...F6GdgW2mG7g%3d

[ratdude747]

Re: Ultra Xfinity 600w 5vsb mod

i forgot about this thread

in another thread, a new idea was posted to fix the issue. is there any way a high esr poly cap could be used to fix the issue without all the work required by this method? or would that introduce new issues?

[everell]

Re: Ultra Xfinity 600w 5vsb mod

LAST STEPS!

Next step is to correct the optoisolator chip wiring. Remove the resistor (labeled R3) which is connected to pin 3 of the optoisolator chip. Insert a jumper wire between Optoisolator pin 3 (using one of the holes resistor R3 was in) and common.

Remove capacitor C4 and Resistor R4 which are connected to pin 4 of the optoisolator. Connect the brown wire from the DM311 board to the optoisolator pin 4 (using hole where C4 or R4 was).

Connect the green wire from the DM311 board to common using any unused "common" hole on the pc board.

Connect the red wire from the DM311 board to any unused +320 volt hole on the pc board.

If you can't find an unused hole for the common or +320 volt connection, I use a Dremel drill and a #60 drill bit to make whatever holes are necessary.

[everell]

Re: Ultra Xfinity 600w 5vsb mod

Next, connect the yellow wire from the DM311 board to the 5vsb feedback winding where you made the trace cut. See drawing below.

[everell]

Re: Ultra Xfinity 600w 5vsb mod

The feedback winding is the winding that is left. Study this circuit carefully.

There should be a diode (labeled D4) between one side of the winding and common. Remove the diode and insert a piece of jumper wire where the diode was.

Using an Xacto knife, cut the circuit trace between the other side of the winding and pin 4 of the optoisolator chip. Make the cut such that the circuit trace path between optoisolator pin 4 and capacitor C4 and resistor R4 is left intact.